Digital music exposure reliably induces temporary threshold shift in normal-hearing human subjects

Serum Prestin Level May Increase Following Music Exposure That Induces Temporary Threshold Shifts: A Pilot Study

OBJECTIVES

To determine if blood prestin level changes after exposure to music at high sound pressure levels, and if this change is associated with temporary threshold shift (TTS) and/or changes in distortion product (DP) amplitude.

DESIGN

Participants were exposed to pop-rock music at 100 dBA for 15 min monaurally through headphones. Pure-tone audiometry, DP amplitude, and blood prestin level were measured before and after exposure.

RESULTS

Fourteen adults (9 women; age range: 20 to 54 years, median age = 31 [Interquartile ratio = 6.75]) with normal hearing were included in the study. Mean prestin level increased shortly after exposure to music, then returned to baseline within 1 week, although this trend was not observed in all participants. All participants presented TTS or a decrease in DP amplitude in at least one frequency after music exposure. There was a statistically significant average threshold elevation at 4 min postexposure. Statistically significant DP amplitude shifts were observed at 4 and 6 kHz, 2 min following exposure. Mean baseline serum prestin level (mean: 140.00 pg/mL, 95% confidence interval (CI): 125.92 to 154.07) progressively increased following music exposure, reaching a maximum at 2 hr (mean: 158.29 pg/mL, 95% CI: 130.42 to 186.66) and returned to preexposure level at 1 week (mean: 139.18 pg/mL, 95% CI: 114.69 to 163.68). However, after correction for multiple comparisons, mean prestin level showed no statistically significant increase from baseline at any timepoint. No correlation between maximum blood prestin level change and average TTS or distortion product otoacoustic emission amplitude shift was found. However, in an exploratory analysis, TTS at 6 kHz (the frequency at which maximum TTS occurred) decreased significantly as baseline blood prestin level increased.

CONCLUSIONS

The results suggest that blood prestin level may change after exposure to music at high sound pressure levels, although statistical significance was not reached in this relatively small sample after correction. Baseline serum prestin level may also predict the degree of TTS. These findings thus suggest that the role of baseline serum prestin level as a proxy marker of cochlear susceptibility to intense music exposure should be further explored.

Examining the utility of near infrared light as pre-exposure therapy to mitigate temporary noise-induced hearing loss in humans

Introduction

This study sought to determine the effect of Occupational Safety and Health Administration (OSHA) compliant noise on auditory health and assess whether pre-noise near infrared (NIR) light therapy can mitigate the effects of noise exposure.

Methods

Over four visits, participants (n = 30, NCT#: 03834714) with normal hearing completed baseline hearing health assessments followed by exposure to open ear, continuous pink noise at 94 dBA for 15 min. Immediately thereafter, post-noise hearing tests at 3000, 4000, and 6000 Hz and distortion product otoacoustic emissions (DPOAEs) were conducted along with the Modified Rhyme Test (MRT), Masking Level Difference Test (MLD), and Fixed Level Frequency Tests (FLFT) [collectively referred to as the Central and Peripheral Auditory Test Battery (CPATB)] to acquire baseline noise sensitivity profiles. Participants were then randomized to either Active or Sham NIR light therapy for 30 min binaurally to conclude Visit 1. Visit 2 (≥24 and ≤ 48 h from Visit 1) began with an additional 30-min session of Active NIR light therapy or Sham followed by repeat CPATB testing and noise exposure. Post-noise testing was again conducted immediately after noise exposure to assess the effect of NIR light therapy. The remaining visits were conducted following ≥2 weeks of noise rest in a cross-over design (i.e., those who had received Active NIR light therapy in Visits 1 and 2 received Sham therapy in Visits 3 and 4).

Results

Recovery hearing tests and DPOAEs were completed at the end of each visit. Participants experienced temporary threshold shifts (TTS) immediately following noise exposure, with a mean shift of 6.79 dB HL (±6.25), 10.61 dB HL (±6.89), and 7.30 dB HL (±7.25) at 3000, 4000, and 6000 Hz, respectively, though all thresholds returned to baseline at 3000, 4000, and 6000 Hz within 75 min of noise exposure. Paradoxically, Active NIR light therapy threshold shifts were statistically higher than Sham therapy at 3000 Hz (p = 0.04), but no other differences were observed at the other frequencies tested. An age sub-analysis demonstrated that TTS among younger adults were generally larger in the Sham therapy group versus Active therapy, though this was not statistically different. There were no differences in CPATB test results across Active or Sham groups. Finally, we observed no changes in auditory function or central processing following noise exposure, suggestive of healthy and resilient inner ears.

Conclusion

In this study, locally administered NIR prior to noise exposure did not induce a significant protective effect in mitigating noise-induced TTS. Further exploration is needed to implement effective dosage and administration for this promising otoprotective therapy.

Development and Validation of an Efficient and Safe Loud Music Exposure Paradigm

PURPOSE

The purpose of this study was to develop a time-efficient music exposure and testing paradigm that safely creates temporary cochlear dysfunction that could be used in future temporary threshold shift (TTS) studies.

METHOD

A 30-min audio compilation of pop rock music tracks was created. Adult volunteers with normal hearing were then exposed to this music material monaurally through headphones for 30 min at 97 dBA or 15 min at 100 dBA. Levels were measured from the ear of a manikin and are considered to provide an equivalent daily noise dose based on a 3-dB exchange. We assessed the changes in their hearing, by means of distortion product otoacoustic emission (DPOAE) testing, and standard and extended high-frequency pure-tone audiometry before and after exposure. There were 17 volunteers in total. In the first trial, eight volunteers (four females; Mdnage = 31 years [interquartile range, IQR = 4.25]) were included. Although TTS was observed in all eight participants for at least one frequency, a large variation in affected frequencies was observed. To address this issue, the audio material was further remastered to adjust levels across the different frequency bands. Fourteen adults (nine newly recruited and five from the first trial; seven females; Mdnage = 31 years [IQR = 5]) were exposed to the new material.

RESULTS

All but two of 17 participants presented clinically significant TTS or decrease in DPOAE amplitude in at least one frequency. Statistically significant average TTS of 7.43 dB was observed at 6 kHz. There were statistically significant average DPOAE amplitude shifts of -2.55 dB at 4 kHz, -4.97 dB at 6 kHz, and -3.14 dB at 8 kHz. No participant presented permanent threshold shift.

CONCLUSIONS

A monaural music paradigm was developed and shown to induce statistically significant TTS and DPOAE amplitude shifts, without evidence of permanent loss. This realistic and time-efficient paradigm may be considered a viable option for experimental studies of temporary music-induced hearing loss.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.25016471.

Health position paper and redox perspectives - Disease burden by transportation noise

Transportation noise is a ubiquitous urban exposure. In 2018, the World Health Organization concluded that chronic exposure to road traffic noise is a risk factor for ischemic heart disease. In contrast, they concluded that the quality of evidence for a link to other diseases was very low to moderate. Since then, several studies on the impact of noise on various diseases have been published. Also, studies investigating the mechanistic pathways underlying noise-induced health effects are emerging. We review the current evidence regarding effects of noise on health and the related disease-mechanisms. Several high-quality cohort studies consistently found road traffic noise to be associated with a higher risk of ischemic heart disease, heart failure, diabetes, and all-cause mortality. Furthermore, recent studies have indicated that road traffic and railway noise may increase the risk of diseases not commonly investigated in an environmental noise context, including breast cancer, dementia, and tinnitus. The harmful effects of noise are related to activation of a physiological stress response and nighttime sleep disturbance. Oxidative stress and inflammation downstream of stress hormone signaling and dysregulated circadian rhythms are identified as major disease-relevant pathomechanistic drivers. We discuss the role of reactive oxygen species and present results from antioxidant interventions. Lastly, we provide an overview of oxidative stress markers and adverse redox processes reported for noise-exposed animals and humans. This position paper summarizes all available epidemiological, clinical, and preclinical evidence of transportation noise as an important environmental risk factor for public health and discusses its implications on the population level.

Noise-Induced Hearing Threshold Shift Correlated with Body Weight and External-Ear Amplification in Chinchilla: a Preliminary Analysis

BACKGROUND

External-ear amplification (EEA) has been shown to vary from 5-19 dB-A in large datasets of pediatric, adolescent, and adult human participants. However, variable EEA is an overlooked characteristic that likely plays a role in individual noise-induced hearing loss (NIHL) susceptibility. A noise exposure varying 5-19 dB-A translates to high-EEA individuals theoretically experiencing 3-4 times greater NIHL risk than low-EEA individuals.

OBJECTIVE

The purpose of this preliminary analysis was to test the hypothesis that higher EEA is correlated with increased noise-induced threshold shift susceptibility.

DESIGN

Nine chinchillas were exposed to 4-kHz octave-band noise at 89 dB-SPL for 24 h. Auditory brainstem response thresholds were obtained pre-exposure, 24-h post-exposure, and 4-week post-exposure. Relationships between EEA and threshold shift were analyzed.

RESULTS

Open-ear EEA ranged 11-19 dB-SPL, and occluded-ear EEA ranged 10-21 dB-SPL. Higher occluded-ear EEA was correlated with increased NIHL susceptibility (p = 0.04), as was lower body weight (p = 0.01). Male animals exhibited more threshold shift than female animals (p = 0.02), lower body weight than female animals (p = 0.02), and higher occluded-ear EEA (male mean = 18 dB; female mean = 15 dB).

CONCLUSIONS

Taken together, increased threshold shift susceptibility was observed in the smallest animals, animals with the highest occluded-ear EEA, and in male animals (which tended to have higher occluded-ear EEA). Given the established relationship between smaller body size and higher occluded-ear EEA, these preliminary results suggest that body size (and occluded-ear EEA; a function of body size) could be a potential, underlying driver of NIHL susceptibility differences, rather than true sex differences.

Prevention of Noise-Induced Hearing Loss Using Investigational Medicines for the Inner Ear: Previous Trial Outcomes Should Inform Future Trial Design

Significance: Noise-induced hearing loss (NIHL) is an important public health issue resulting in decreased quality of life for affected individuals, and significant costs to employers and governmental agencies. Recent Advances: Advances in the mechanistic understanding of NIHL have prompted a growing number of proposed, in-progress, and completed clinical trials for possible protections against NIHL via antioxidants and other drug agents. Thirty-one clinical trials evaluating prevention of either temporary or permanent NIHL were identified and are reviewed. Critical Issues: This review revealed little consistency in the noise-exposed populations in which drugs are evaluated or the primary outcomes used to measure NIHL prevention. Changes in pure-tone thresholds were the most common primary outcomes; specific threshold metrics included both average hearing loss and incidence of significant hearing loss. Changes in otoacoustic emission (OAE) amplitude were relatively common secondary outcomes. Extended high-frequency (EHF) hearing and speech-in-noise perception are commonly adversely affected by noise exposure but are not consistently included in clinical trials assessing prevention of NIHL. Future Directions: Multiple criteria are available for monitoring NIHL, but the specific criterion to be used to define clinically significant otoprotection remains a topic of discussion. Audiogram-based primary outcome measures can be combined with secondary outcomes, including OAE amplitude, EHF hearing, speech-in-noise testing, tinnitus surveys, and patient-reported outcomes. Standardization of test protocols for the above primary and secondary outcomes, and associated reporting criterion for each, would facilitate clinical trial design and comparison of results across investigational drug agents. Antioxid. Redox Signal. 36, 1171-1202.

The Variability in Potential Biomarkers for Cochlear Synaptopathy After Recreational Noise Exposure

PURPOSE

Speech-in-noise tests and suprathreshold auditory evoked potentials are promising biomarkers to diagnose cochlear synaptopathy (CS) in humans. This study investigated whether these biomarkers changed after recreational noise exposure.

METHOD

The baseline auditory status of 19 normal-hearing young adults was analyzed using questionnaires, pure-tone audiometry, speech audiometry, and auditory evoked potentials. Nineteen subjects attended a music festival and completed the same tests again at Day 1, Day 3, and Day 5 after the music festival.

RESULTS

No significant relations were found between lifetime noise-exposure history and the hearing tests. Changes in biomarkers from the first session to the follow-up sessions were nonsignificant, except for speech audiometry, which showed a significant learning effect (performance improvement).

CONCLUSIONS

Despite the individual variability in prefestival biomarkers, we did not observe changes related to the noise-exposure dose caused by the attended event. This can indicate the absence of noise exposure-driven CS in the study cohort, or reflect that biomarkers were not sensitive enough to detect mild CS. Future research should include a more diverse study cohort, dosimetry, and results from test-retest reliability studies to provide more insight into the relationship between recreational noise exposure and CS. Supplemental Material https://doi.org/10.23641/asha.16821283.

Sports audiology: Ear hygiene practices of gym users who wear earphones

BACKGROUND

Technological advancements have facilitated the demand for electronic systems to track and measure progress during exercise activities. Electronic devices with music applications, such as iPods and smartphones, are popular during gym sessions as they support the ambiance to one's exercise programme. Earphones are the popular choice for the transmission of music to the gym user's ear. There is a direct correlation between the cardiovascular health and the aural health because of the effect of increased blood supply to the auditory system. Therefore, this research study explores the ear hygiene of gym users.

OBJECTIVES

This study aimed at determining the ear hygiene and middle-ear status of gym users who wore earphones whilst exercising.

METHOD

A purposive sampling method was adopted. Data were collected in two phases: phase 1 via a questionnaire and phase 2 included an otoscopic examination and tympanometry. Qualitative and quantitative data were analysed.

RESULTS

Fifty-four participants were included. Ear hygiene was not a priority for all gym users. The results revealed that 87% of the participants randomly cleaned their ears; however, 59% were cleaning their earphones. The middle ear assessment indicated that 17% of the participants presented with pathological indicators. Participants requested for the implementation of educational programmes pertaining to infection control measures for proper ear hygiene.

CONCLUSION

There is a dearth of health and wellness educational programmes that include ear hygiene practices, necessitating the development of prevention and promotion programmes for this niche area in audiology. The need for guidelines pertaining to ear hygiene practices amongst gym users is vital to ensure that the auditory system is monitored and protected when individuals participate in exercise sessions.

Modeling individual noise-induced hearing loss risk with proxy measurements of external-ear amplification

Significant variability in noise-induced hearing loss (NIHL) susceptibility suggests there are factors beyond sound level and duration of exposure that contribute to individual susceptibility. External-ear amplification (EEA) from external-ear structures varies significantly due to ear size and shape, potentially influencing NIHL susceptibility. This study tested the hypothesis that EEA can be predicted using non-technical proxy measurements including pinna height (cm), body height (m), and earcanal volume (cm³). 158 participants (4-78 years) completed otoscopy, tympanometry, pinna measurements, body height measurements, and two EEA measurements: (1) total real-ear unaided gain (REUG) of the open ear and (2) real-ear to coupler difference (RECD), representing unaided gain from the earcanal. Participants' individual noise doses were compared in hypothetical exposures. REUG ranged from 5 to 19 dBA and was correlated with pinna height. High-REUG participants were estimated to accrue noise doses at least 5 times higher than low-REUG participants. RECD ranged from 7 to 24 dBA and was correlated with earcanal volume and body height. The results support the hypothesis that EEA measurement could significantly improve estimation of an individual's position along the NIHL risk spectrum. Non-technical proxy measurements of EEA (pinna height, body height, earcanal volume) were statistically significant but yielded high variability in individual EEA prediction.

Patterns of noise exposure and prevalence of hearing loss amongst Cape Town Minstrel Carnival musicians

Background

Cape Town Minstrel Carnival is one of the oldest and most authentic indigenous New Year’s customs in South Africa. Musicians who perform at this carnival are exposed to excessively loud music and therefore at a risk of acquiring noise-induced hearing loss (NIHL).

Objectives

This study aimed to determine patterns of exposure to loud music and prevalence of hearing loss amongst Cape Town Minstrel Carnival musicians.

Method

A descriptive, observational exploratory survey design was used and 43 participants (21 males and 22 females; mean age, 21 ± 9 years) took part in this study. Sound level measurements were conducted to assess musicians’ sound exposure during rehearsals and performances. All participants underwent the following audiological test battery at least 2 h before music exposure: Case history, otoscopic examination, tympanometry, pure tone audiometry and distortion products otoacoustic emission (DPOAE).

Results

Average noise levels recorded were 86 dBA during rehearsals and 98.7 dBA at performances and average durations of exposure were 240 and 10 min at rehearsals and performances, respectively. One out of 43 (1/43) participants presented with sensorineural hearing loss. Audiometric results of the remaining participants were normal and did not show a pattern suggestive of NIHL. A high proportion of participants (21/43) reported experiencing tinnitus.

Conclusion

Despite being exposed to high levels of noise, there was a low prevalence of hearing loss amongst these musicians. However, a high proportion of them reported tinnitus, which could be an indication that they were at a high risk of NIHL from the music that they played.

Loud Music and Leisure Noise Is a Common Cause of Chronic Hearing Loss, Tinnitus and Hyperacusis

High sound levels capable of permanently damaging the ear are experienced not only in factories and war zones but in concert halls, nightclubs, sports stadiums, and many other leisure environments. This review summarizes evidence that loud music and other forms of "leisure noise" are common causes of noise-induced hearing loss, tinnitus, and hyperacusis, even if audiometric thresholds initially remain within clinically normal limits. Given the huge global burden of preventable noise-induced hearing loss, noise limits should be adopted in a much broader range of settings, and education to promote hearing conservation should be a higher public health priority.

Acute Recreational Noise-Induced Cochlear Synaptic Dysfunction in Humans With Normal Hearing: A Prospective Cohort Study

Objectives

The objective of the study was to identify the acute high-intensity recreational noise-induced effects on auditory function, especially the cochlear synaptopathy-related audiological metrics, in humans with normal hearing.

Methods

This prospective cohort study enrolled 32 young adults (14 males and 18 females); the mean age was 24.1 ± 2.4 years (ranging from 20 to 29). All participants with normal hearing (audiometric thresholds ≤25 dB HL at frequencies of 0.25, 0.5, 1, 2, 3, 4, 6, and 8 kHz for both ears) had already decided to participate in the outdoor music festival. Participants were asked to measure the noise exposure dose and complete auditory examinations, including the air-conduction pure-tone audiometry (PTA), distortion product otoacoustic emission (DPOAE), contralateral suppression (CS) on transient evoked otoacoustic emission (TEOAE), auditory brainstem response (ABR) test and Mandarin Hearing in Noise Test (MHINT), at baseline and 1 day and 14 days after music festival noise exposure.

Results

The mean time of attending the music festival was 7.34 ± 0.63 h (ranging from 6.4 to 9.5), the mean time-weighted average (TWA) of noise exposure dose was 93.2 ± 2.39 dB(A) (ranging from 87.9 to 97.7). At neither 1 day nor 14 days post exposure, there were no statistically significant effects on PTA thresholds, DPOAE amplitudes, CS on TEOAEs, or MHINT signal-to-noise ratios (SNRs) of acute outdoor music festival noise exposure, regardless of sex. While the ABR wave I amplitudes significantly decreased at 1 day after exposure and recovered at 14 days after exposure, the exposed/unexposed ABR wave I amplitude ratio was significantly correlated with MHINT SNR change at 1 day after exposure, although it was not correlated with the noise exposure dose.

Conclusion

In young adults with normal hearing, we found the self-compared decrement of ABR wave I amplitudes at 1 day post acute recreational noise exposure at high intensity, which also contributes to the change in speech perceptual ability in noisy backgrounds. This study indicated that auditory electrophysiological metric changes might be a more sensitive and efficient indicator of noise-induced cochlear synaptic dysfunction in humans. More attention should be paid to the recreational noise-induced cochlear synaptopathy and auditory perceptual disorder.

Temporary Threshold Shifts among Iron and Steel Factory Workers in Tanzania: A Pre-Interventional Study

Background

Workers in iron and steel factories in Tanzania are exposed to noise levels above recommended limit values, without using hearing protection devices. Exposure to noise levels above 85 dB(A) is associated with temporary threshold shifts (TTS) of human hearing. Nevertheless, there are few studies of noise and hearing from African countries.

Objective

To determine whether the normal hearing workers in Tanzania experiences TTS after full-shift occupational noise exposure of 85 dB(A) and above.

Methods

A total of 55 workers were included. Full-shift personal noise measurements were conducted. Pre- and post-shifts pure-tone audiometry were conducted for each worker. TTS was defined as a 10 dB or greater change at 1000, 2000, 3000 or 4000 Hz in either ear.

Results

We found that 85.5% of the workers developed TTS across the work shift. There was significant increase in mean hearing thresholds across shift at 1000, 2000, 3000 and 4000 Hz among the workers exposed to an average personal noise exposure (LAeq,8h) of 90.4 dB(A) (SD = 2.7). The difference in mean hearing thresholds was higher at 4000 Hz [Arithmetic Mean (AM) = 10 dB SD = 4 dB] compared to that of 1000 Hz (AM = 4 dB SD = 3 dB), 2000 Hz (AM = 4 dB SD = 4 dB), and 3000 Hz (AM = 9 dB SD = 6 dB), respectively.

Conclusions

Interventions to reduce occupational personal noise exposure are warranted to reduce the high risk of developing a permanent threshold shift with persistent high noise exposure. An intervention study is planned for this group of workers.

Rehearsal Sound Exposure and Choir Singers' Hearing: A Pilot Field Study

Exposure to high- and moderate-intensity sound is inevitable for professional singers during their working day, the majority of which is spent in rehearsal, preparing for a performance. The impact of self-produced sound exposure on singers' hearing within the rehearsal setting has not been examined.

OBJECTIVES

This original pilot field study investigates the feasibility of data collection and hypothesis testing of singers' hearing within the rehearsal environment.

METHODS

18 professional choir singers are examined for hearing threshold changes following routine rehearsal sound exposure. Pure Tone Audiometry is measured before, immediately after, and approximately 24 hours after rehearsal.

RESULTS

This study does not identify definitive Temporary Threshold Shift in this population under these conditions. That said, mean temporary threshold shift was found 3.61 dB higher than the recovery threshold shift in the right ear at 3000 Hz (P = 0.06), and this may be important to look at for future studies.

CONCLUSIONS

Methodological challenges of this field study include dynamic experimental conditions intrinsic to the rehearsal process, environmental and musical influence on Pure Tone Audiometry results and estimation of sound intensity exposure.

Temporary Hearing Loss and Associated Factors Among Ayka Addis Textile Factory Workers in Oromia Region, Ethiopia: A Cross-Sectional Study

INTRODUCTION

The development of modern automated machines in industries has considerably decreased the physical burden of workers in addition to increasing the productivity of the industries resulting in noise pollution. Noise exposure above the limit value of 90 dB (A) is known to cause temporary hearing loss among exposed workers.

MATERIALS AND METHODS

Institutional-based cross-sectional study design was employed for a total of 406 study participants using a simple random sampling technique from January 15 to April 30, 2019. The data collection methods were observational checklist and a self-administered questionnaire. The collected data were entered into EpiData software version 4.2 and exported to SPSS software version 21 for analysis. Bivariate and multivariable logistic analyses wwere used to identify the associated factors. Statistical significance was declared using a 95% confidence interval and a p-value of less than 0.05.

RESULTS

A total of 388 study participants were included in the study with a response rate of 95.6%, of which 254 (65.5%) were females. The overall temporary hearing loss among the textile factory workers was found to be 49% with COR=1.53; 95% CI (1.15-2.03). The workers from the spinning department were 2.38 times more likely to develop temporary hearing loss after exiting from work than workers from the dyeing department (95% CI= (1.16-4.90). Similarly, workers from the knitting department were 3.67 times more likely to develop temporary hearing loss after exiting from work than workers from the dyeing department (95% CI=1.42-9.47).

CONCLUSION

The present study demonstrated that the workforce in the spinning and knitting departments of the textile factory had a high prevalence of temporary hearing loss than the workers in dyeing and garment working sections. Therefore, the textile factory should provide hearing protection devices to the workers.

The Effects of Short-Term and Long-term Hearing Changes on Music Exposure: A Systematic Review and Meta-Analysis

The present study explores the scientific evidence on whether music exposure temporarily or permanently affects hearing sensitivity in young adults. Six electronic databases were searched using related keywords for the four categories of personal listening devices, listening habits, hearing outcomes, and age. The Hedges’ g and its 95% confidence intervals (CIs) were estimated. A Higgins I² was also used to check for heterogeneity. To test for publication bias, funnel plots were drawn using Egger’s regression. Based on the inclusion criteria, 16 studies were divided into two groups to identify short-term hearing changes (n = 7) and long-term hearing changes (n = 9). In the short term, there was no significant immediate change in the thresholds or amplitudes after the music exposure, although pure-tone thresholds (PTAs) and distortion product otoacoustic emissions (DPOAEs) did show the highest effect size (−0.344, CI −0.727 to 0.038) and (0.124, CI −0.047 to 0.296) at 4 kHz. On the other hand, for long-term hearing changes, the PTA provided the highest effect size at 6 kHz (−0.525, CI −0.897 to −0.154) and 8 kHz (–0.486, CI −0.819 to −0.152), while also implying that habitual and repeated personal listening device (PLD) usage can act on some significant hearing changes in audiological tests. We conclude that the use of a PLD produces a few temporary hearing changes at 4 kHz after its use but that the changes are then reversed. However, it is important to note heavy PLD users’ experience regarding permanent changes in their hearing thresholds at high frequencies, and the public should be educated on this issue.

Exploring the association of Bone Alkaline Phosphatases And Hearing Loss

Hearing loss becomes increasingly common with age and affects quality of life. Recently, scientists have published articles about the relationship between metabolic disease and hearing loss. Metabolic disease was previously found to be highly related to an increase in alkaline phosphatase. Thus, there may be an indirect relationship between alkaline phosphatase (ALP) and hearing loss. In this paper, we will demonstrate the relationship between ALP and hearing loss. We included 3877 National Health and Nutrition Examination Survey (NHANES) participants, who represent the noninstitutionalized civilian population in the United States from age 20 to age 69, and examined the association between ALP and frequency distributions of pure-tone air-condition (PTAC) thresholds. After adjusting for pertinent variables, the subjects who belonged to the higher quartiles of ALP tended to have worse hearing thresholds (pure tone average at high and low frequencies) than the first quartile of ALP (p < 0.001). The results showed a positive correlation between ALP and hearing loss, in both males and females (p < 0.001) and in subjects whose body mass indices (BMI) were less than 30 (p < 0.001). In conclusion, ALP may play a role in detecting hearing loss.

Noise-dose estimated with and without pre-cochlear amplification

Amplification from natural ear canal resonance has been documented as highly variable across individuals. However, individual variability in total pre-cochlear amplification (i.e., combined external and middle ear mechanisms) remains understudied in relevance to noise-induced hearing loss (NIHL). It is well-known that more noise means more risk of hearing loss, yet the current risk-models do not consider individually variable pre-cochlear amplification, also referred to as the transfer function of the open ear (TFOE). The present study principally documented individual TFOE variability and explored the feasibility and accuracy of simple proxy metrics, which could be used to estimate TFOE. Participants' TFOE values were used to estimate their NIHL risk in hypothetical free-field exposures. Forty-eight adult participants (42 female, 6 male, ages 21-60 years) met inclusion criteria of 2 healthy pinnae and ear canals (<10% cerumen occlusion) and type-A tympanometric examination. Participants underwent otoscopy, tympanometry, pinna size measurement, real-ear-to-coupler-difference, and TFOE measurement. TFOE ranged from 5 to 15 dB-A (mean = 10 dB-A); given that NIHL risk is estimated to double in either 3 or 5 dB-A increments, the observed variability could explain a substantial portion of individual vulnerability to NIHL. A simple regression model with eardrum compliance (ml) was correlated with individual TFOE (p < 0.05). TFOE variability has the potential to substantially explain why two individuals with the same noise-exposure can develop significantly different degrees of NIHL. Eardrum compliance (ml) was a correlated proxy measurement of TFOE in this principally adult, female dataset; additional research is needed to confirm this relationship in a unique, heterogeneous dataset.

Noise-induced hearing loss and its prevention: Integration of data from animal models and human clinical trials

Animal models have been used to gain insight into the risk of noise-induced hearing loss (NIHL) and its potential prevention using investigational new drug agents. A number of compounds have yielded benefit in pre-clinical (animal) models. However, the acute traumatic injury models commonly used in pre-clinical testing are fundamentally different from the chronic and repeated exposures experienced by many human populations. Diverse populations that are potentially at risk and could be considered for enrollment in clinical studies include service members, workers exposed to occupational noise, musicians and other performing artists, and children and young adults exposed to non-occupational (including recreational) noise. Both animal models and clinical populations were discussed in this special issue, followed by discussion of individual variation in vulnerability to NIHL. In this final contribution, study design considerations for NIHL otoprotection in pre-clinical and clinical testing are integrated and broadly discussed with evidence-based guidance offered where possible, drawing on the contributions to this special issue as well as other existing literature. The overarching goals of this final paper are to (1) review and summarize key information across contributions and (2) synthesize information to facilitate successful translation of otoprotective drugs from animal models into human application.

The use of nonhuman primates in studies of noise injury and treatment

Exposure to prolonged or high intensity noise increases the risk for permanent hearing impairment. Over several decades, researchers characterized the nature of harmful noise exposures and worked to establish guidelines for effective protection. Recent laboratory studies, primarily conducted in rodent models, indicate that the auditory system may be more vulnerable to noise-induced hearing loss (NIHL) than previously thought, driving renewed inquiries into the harmful effects of noise in humans. To bridge the translational gaps between rodents and humans, nonhuman primates (NHPs) may serve as key animal models. The phylogenetic proximity of NHPs to humans underlies tremendous similarity in many features of the auditory system (genomic, anatomical, physiological, behavioral), all of which are important considerations in the assessment and treatment of NIHL. This review summarizes the literature pertaining to NHPs as models of hearing and noise-induced hearing loss, discusses factors relevant to the translation of diagnostics and therapeutics from animals to humans, and concludes with some of the practical considerations involved in conducting NHP research.

Risk of noise-induced hearing loss due to recreational sound: Review and recommendations

This review was conducted to address three questions related to recreational sound exposure: (1) what criteria are used to determine noise exposure limits, (2) are there differences in the risk of hearing loss from occupational noise versus recreational sound, and (3) what is an appropriate exposure limit for recreational sound? For the first question, most standards specify an 8-h occupational noise exposure limit (L_EX) of 85 dBA. This limit assumes that some workers exposed at the limit will develop hearing loss. To eliminate the risk of hearing loss, a 24-h equivalent continuous level (L_EQ24h) limit of 70 dBA is appropriate. For the second question, there is some evidence that the effects of occupational noise on hearing may be worse than energetically equivalent recreational sound. Limits developed for noise are nevertheless applicable to recreational sound, and use of existing statistical models to predict hearing loss from recreational sound is appropriate, with the caveat that these models are limited to durations ≤40 years. For the third question, a recreational sound limit of 80 dBA L_EX, equivalent to a 75 dBA L_EQ24h, will virtually eliminate the risk of recreationally induced hearing loss in adults. Lower limits may be warranted for vulnerable or susceptible individuals.

Assessment of Safe Listening Intentional Behavior Toward Personal Listening Devices in Young Adults

Recreational noise-induced hearing loss (RNIHL) is a highly preventable disorder that is commonly seen in teenagers and young adults. Despite the documented negative effects of RNIHL, it is still challenging to persuade people to adopt safe listening behaviors. More research is needed to understand the underlying factors guiding listeners’ intentions to engage in safe listening habits. We used the Theory of Planned Behavior (TPB) to identify attitudes, social norms, and behavioral control in 92 young adults toward two intentional behaviors related to safe listening habits while listening to their personal listening devices: (1) lowering the intensity of loud music, and (2) shortening the listening duration of loud music. Using a Qualtrics survey, the major factors of the TPB model as they relate to the participants’ intention to engage in risk-controlling behavior were assessed. Behavioral intentions to turn the music down and listen for shorter durations were thought to be predicted by the TPB factors (attitudes, social norms, and perceived behavioral control). Linear regression findings indicated that the overall TPB models were significant. Positive attitudes toward turning the music down and shortening the durations were significantly associated with intentions to engage in non-risky behavior, more so for the former behavior.

Otoprotectants: From Research to Clinical Application

There is an urgent need for otoprotective drug agents. Prevention of noise-induced hearing loss continues to be a major challenge for military personnel and workers in a variety of industries despite the requirements that at-risk individuals use hearing protection devices such as ear plugs or ear muffs. Drug-induced hearing loss is also a major quality-of-life issue with many patients experiencing clinically significant hearing loss as a side effect of treatment with life-saving drug agents such as cisplatin and aminoglycoside antibiotics. There are no pharmaceutical agents approved by the United States Food and Drug Administration for the purpose of protecting the inner ear against damage, and preventing associated hearing loss (otoprotection). However, a variety of preclinical studies have suggested promise, with some supporting data from clinical trials now being available as well. Additional research within this promising area is urgently needed.

No Reliable Association Between Recreational Noise Exposure and Threshold Sensitivity, Distortion Product Otoacoustic Emission Amplitude, or Word-in-Noise Performance in a College Student Population

OBJECTIVES

The purpose of this study was to evaluate the relationship between recreational sound exposure and potentially undiagnosed or subclinical hearing loss by assessing sound exposure history, threshold sensitivity, distortion product otoacoustic emission (DPOAE) amplitudes, and performance on the words-in-noise (WIN) test.

DESIGN

Survey data were collected from 74 adult participants (14 male and 60 female), 18 to 27 years of age, recruited via advertisements posted throughout the University of Florida campus. Of these participants, 70 completed both the survey and the additional functional test battery, and their preferred listening level was measured in a laboratory setting.

RESULTS

There were statistically significant relationships between hearing thresholds and DPOAE amplitude. In contrast, performance on the WIN was not reliably related to threshold sensitivity within this cohort with largely normal hearing. The two most common exposures included bars or dance clubs, followed by music player use. There were no statistically significant relationships between individual or composite measures of recreational sound exposure, including preferred listening level, years of music player use, number of reported sound exposures, previous impulse noise exposure, or previous noise-induced change in hearing, and functional measures including threshold, DPOAE amplitude, and WIN measures. Some subjects were highly consistent in listening level preferences, while others were more variable from song to song.

CONCLUSIONS

No reliable relationships between common recreational sound exposure or previous noise-induced changes in hearing were found during analysis of threshold sensitivity, DPOAE amplitude, or WIN performance in this cohort. However, the study sample was predominantly female and Caucasian, which limits generalizability of the results.

Is exposure to personal music players a confounder in adolescent mobile phone use and hearing health studies?

Objective

This study was performed to determine whether exposure to personal music players (PMPs) in the immediate morning prior to hearing testing confounds the association between mobile phone use and hearing thresholds of adolescents.

Design

In this cohort study of cognitive function in year 7 students (median age 13 years, range 11–14), information regarding the weekly use of mobile phones and the use of PMPs was assessed by a questionnaire. Pure-tone audiometry was used to establish hearing thresholds for all participants.

Results

Among a cohort of 317 adolescents (60.9% females), 130 were unexposed to PMP use while 33 were exposed to PMP use in the morning prior to hearing testing. No statistically significant difference in hearing threshold shifts was found between adolescents who were and were not exposed to PMP use prior to hearing testing. Likewise, the difference in the use of mobile phones according to the PMP use status was not statistically significant.

Conclusion

Exposure to PMPs prior to hearing testing did not introduce confounding in the present study of mobile phone use and hearing loss among adolescents.

Sound pressure levels generated at risk volume steps of portable listening devices: types of smartphone and genres of music

Background

The present study estimated the sound pressure levels of various music genres at the volume steps that contemporary smartphones deliver, because these levels put the listener at potential risk for hearing loss.

Methods

Using six different smartphones (Galaxy S6, Galaxy Note 3, iPhone 5S, iPhone 6, LG G2, and LG G3), the sound pressure levels for three genres of K-pop music (dance-pop, hip-hop, and pop-ballad) and a Billboard pop chart of assorted genres were measured through an earbud for the first risk volume that was at the risk sign proposed by the smartphones, as well as consecutive higher volumes using a sound level meter and artificial mastoid.

Results

The first risk volume step of the Galaxy S6 and the LG G2, among the six smartphones, had the significantly lowest (84.1 dBA) and highest output levels (92.4 dBA), respectively. As the volume step increased, so did the sound pressure levels. The iPhone 6 was loudest (113.1 dBA) at the maximum volume step. Of the music genres, dance-pop showed the highest output level (91.1 dBA) for all smartphones. Within the frequency range of 20~ 20,000 Hz, the sound pressure level peaked at 2000 Hz for all the smartphones.

Conclusions

The results showed that the sound pressure levels of either the first volume step or the maximum volume step were not the same for the different smartphone models and genres of music, which means that the risk volume sign and its output levels should be unified across the devices for their users. In addition, the risk volume steps proposed by the latest smartphone models are high enough to cause noise-induced hearing loss if their users habitually listen to music at those levels.

Effects of Recreational Noise on Threshold and Suprathreshold Measures of Auditory Function

Noise exposure that causes a temporary threshold shift but no permanent threshold shift can cause degeneration of synaptic ribbons and afferent nerve fibers, with a corresponding reduction in wave I amplitude of the auditory brainstem response (ABR) in animals. This form of underlying damage, hypothesized to also occur in humans, has been termed synaptopathy , and it has been hypothesized that there will be a hidden hearing loss consisting of functional deficits at suprathreshold stimulus levels. This study assessed whether recreational noise exposure history was associated with smaller ABR wave I amplitude and poorer performance on suprathreshold auditory test measures. Noise exposure histories were collected from 26 men and 34 women with hearing thresholds ≤ 25 dB hearing loss (HL; 250 Hz to 8 kHz), and a variety of functional suprathreshold hearing tests were performed. Wave I amplitudes of click-evoked ABR were obtained at 70, 80, 90, and 99 dB (nHL) and tone-burst evoked ABR were obtained at 90 dB nHL. Speech recognition performance was measured in quiet and in competing noise, using the Words in Noise test, and the NU-6 word list in broadband noise (BBN). In addition, temporal summation to tonal stimuli was assessed in quiet and in competing BBN. To control for the effects of subclinical conventional hearing loss, distortion product otoacoustic emission amplitude, an indirect measure of outer hair cell integrity, was measured. There was no statistically significant relationship between noise exposure history scores and ABR wave I amplitude in either men or women for any of the ABR conditions. ABR wave I amplitude and noise exposure history were not reliably correlated with suprathreshold functional hearing tests. Taken together, this study found no evidence of noise-induced decreases in ABR wave I amplitude or signal processing in noise in a cohort of subjects with a history of recreational noise exposure.

Safety and efficacy of ebselen for the prevention of noise-induced hearing loss: a randomised, double-blind, placebo-controlled, phase 2 trial

BACKGROUND

Noise-induced hearing loss is a leading cause of occupational and recreational injury and disease, and a major determinant of age-related hearing loss. No therapeutic agent has been approved for the prevention or treatment of this disorder. In animal models, glutathione peroxidase 1 (GPx1) activity is reduced after acute noise exposure. Ebselen, a novel GPx1 mimic, has been shown to reduce both temporary and permanent noise-induced hearing loss in preclinical studies. We assessed the safety and efficacy of ebselen for the prevention of noise-induced hearing loss in young adults in a phase 2 clinical trial.

METHODS

In this single-centre, randomised, double-blind, placebo-controlled phase 2 trial, healthy adults aged 18-31 years were randomly assigned (1:1:1:1) at the University of Florida (Gainsville, FL, USA) to receive ebselen 200 mg, 400 mg, or 600 mg, or placebo orally twice daily for 4 days, beginning 2 days before a calibrated sound challenge (4 h of pre-recorded music delivered by insert earphones). Randomisation was done with an allocation sequence generated by an independent third party. The primary outcome was mean temporary threshold shift (TTS) at 4 kHz measured 15 min after the calibrated sound challenge by pure tone audiometry; a reduction of 50% in an ebselen dose group compared with the placebo group was judged to be clinically relevant. All participants who received the calibrated sound challenge and at least one dose of study drug were included in the efficacy analysis. All randomly assigned patients were included in the safety analysis. This trial is registered with ClinicalTrials.gov, number NCT01444846.

FINDINGS

Between Jan 11, 2013, and March 24, 2014, 83 participants were enrolled and randomly assigned to receive ebselen 200 mg (n=22), 400 mg (n=20), or 600 mg (n=21), or placebo (n=20). Two participants in the 200 mg ebselen group were discontinued from the study before the calibrated sound challenge because they no longer met the inclusion criteria; these participants were excluded from the efficacy analysis. Mean TTS at 4 kHz was 1·32 dB (SE 0·91) in the 400 mg ebselen group compared with 4·07 dB (0·90) in the placebo group, representing a significant reduction of 68% (difference -2·75 dB, 95% CI -4·54 to -0·97; p=0·0025). Compared with placebo, TTS at 4 kHz was non-significantly reduced by 21% in the 200 mg ebselen group (3·23 dB [SE 0·91] vs 4·07 dB [0·90] in the placebo group; difference -0·84 dB, 95% CI -2·63 to 0·94; p=0·3542) and by 7% in the 600 mg ebselen group (3·81 dB [0·90] vs 4·07 dB [0·90] in the placebo group; difference -0·27, 95% CI -2·03 to 1·50; p=0·7659). Ebselen treatment was well tolerated across all doses and no significant differences were seen in any haematological, serum chemistry, or radiological assessments between the ebselen groups and the placebo group.

INTERPRETATION

Treatment with ebselen was safe and effective at a dose of 400 mg twice daily in preventing a noise-induced TTS. These data lend support to a role of GPx1 activity in acute noise-induced hearing loss.

FUNDING

Sound Pharmaceuticals.

Hidden Hearing Loss? No Effect of Common Recreational Noise Exposure on Cochlear Nerve Response Amplitude in Humans

This study tested hypothesized relationships between noise exposure and auditory deficits. Both retrospective assessment of potential associations between noise exposure history and performance on an audiologic test battery and prospective assessment of potential changes in performance after new recreational noise exposure were completed.

Methods: 32 participants (13M, 19F) with normal hearing (25-dB HL or better, 0.25–8 kHz) were asked to participate in 3 pre- and post-exposure sessions including: otoscopy, tympanometry, distortion product otoacoustic emissions (DPOAEs) (f2 frequencies 1–8 kHz), pure-tone audiometry (0.25–8 kHz), Words-in-Noise (WIN) test, and electrocochleography (eCochG) measurements at 70, 80, and 90-dB nHL (click and 2–4 kHz tone-bursts). The first session was used to collect baseline data, the second session was collected the day after a loud recreational event, and the third session was collected 1-week later. Of the 32 participants, 26 completed all 3 sessions.

Results: The retrospective analysis did not reveal statistically significant relationships between noise exposure history and any auditory deficits. The day after new exposure, there was a statistically significant correlation between noise “dose” and WIN performance overall, and within the 4-dB signal-to-babble ratio. In contrast, there were no statistically significant correlations between noise dose and changes in threshold, DPOAE amplitude, or AP amplitude the day after new noise exposure. Additional analyses revealed a statistically significant relationship between TTS and DPOAE amplitude at 6 kHz, with temporarily decreased DPOAE amplitude observed with increasing TTS.

Conclusions: There was no evidence of auditory deficits as a function of previous noise exposure history, and no permanent changes in audiometric, electrophysiologic, or functional measures after new recreational noise exposure. There were very few participants with TTS the day after exposure - a test time selected to be consistent with previous animal studies. The largest observed TTS was approximately 20-dB. The observed pattern of small TTS suggests little risk of synaptopathy from common recreational noise exposure, and that we should not expect to observe changes in evoked potentials for this reason. No such changes were observed in this study. These data do not support suggestions that common, recreational noise exposure is likely to result in “hidden hearing loss”.

Noise-induced cochlear synaptopathy in rhesus monkeys (Macaca mulatta)

Cochlear synaptopathy can result from various insults, including acoustic trauma, aging, ototoxicity, or chronic conductive hearing loss. For example, moderate noise exposure in mice can destroy up to ∼50% of synapses between auditory nerve fibers (ANFs) and inner hair cells (IHCs) without affecting outer hair cells (OHCs) or thresholds, because the synaptopathy occurs first in high-threshold ANFs. However, the fiber loss likely impairs temporal processing and hearing-in-noise, a classic complaint of those with sensorineural hearing loss. Non-human primates appear to be less vulnerable to noise-induced hair-cell loss than rodents, but their susceptibility to synaptopathy has not been studied. Because establishing a non-human primate model may be important in the development of diagnostics and therapeutics, we examined cochlear innervation and the damaging effects of acoustic overexposure in young adult rhesus macaques. Anesthetized animals were exposed bilaterally to narrow-band noise centered at 2 kHz at various sound-pressure levels for 4 h. Cochlear function was assayed for up to 8 weeks following exposure via auditory brainstem responses (ABRs) and otoacoustic emissions (OAEs). A moderate loss of synaptic connections (mean of 12-27% in the basal half of the cochlea) followed temporary threshold shifts (TTS), despite minimal hair-cell loss. A dramatic loss of synapses (mean of 50-75% in the basal half of the cochlea) was seen on IHCs surviving noise exposures that produced permanent threshold shifts (PTS) and widespread hair-cell loss. Higher noise levels were required to produce PTS in macaques compared to rodents, suggesting that primates are less vulnerable to hair-cell loss. However, the phenomenon of noise-induced cochlear synaptopathy in primates is similar to that seen in rodents.

A faceoff with hazardous noise: Noise exposure and hearing threshold shifts of indoor hockey officials

Noise exposure and hearing thresholds of indoor hockey officials of the Western States Hockey League were measured to assess the impact of hockey game noise on hearing sensitivity. Twenty-nine hockey officials who officiated the league in an arena in southeastern Wyoming in October, November, and December 2014 participated in the study. Personal noise dosimetry was conducted to determine if officials were exposed to an equivalent sound pressure level greater than 85 dBA. Hearing thresholds were measured before and after hockey games to determine if a 10 dB or greater temporary threshold shift in hearing occurred. Pure-tone audiometry was conducted in both ears at 500, 1000, 2000, 3000, 4000, 6000, and 8000 Hz. All noise exposures were greater than 85 dBA, with a mean personal noise exposure level of 93 dBA (SD = 2.2), providing 17.7% (SD = 6.3) of the officials' daily noise dose according to the OSHA criteria. Hearing threshold shifts of 10 dB or greater were observed in 86.2% (25/29) of officials, with 36% (9/25) of those threshold shifts equaling 15 dB or greater. The largest proportion of hearing threshold shifts occurred at 4000 Hz, comprising 35.7% of right ear shifts and 31.8% of left ear shifts. The threshold shifts between the pre- and post-game audiometry were statistically significant in the left ear at 500 (p=.019), 2000 (p=.0009), 3000 (p<.0001) and 4000 Hz (p=.0002), and in the right ear at 2000 (p=.0001), 3000 (p=.0001) and 4000 Hz (p<.0001), based on Wilcoxon-ranked sum analysis. Although not statistically significant at alpha = 0.05, logistic regression indicated that with each increase of one dB of equivalent sound pressure measured from personal noise dosimetry, the odds of a ≥ 10 dB TTS were increased in the left ear at 500 (OR=1.33, 95% CI 0.73-2.45), 3000 (OR=1.02, 95% CI 0.68-1.51), 4000 (OR=1.26, 95% CI 0.93-1.71) and 8000 Hz (OR=1.22, 95% CI 0.76-1.94) and in the right ear at 6000 (OR=1.03, 95% CI 0.14-7.84) and 8000 Hz (OR=1.29, 95% CI 0.12-13.83). These findings suggest that indoor hockey officials are exposed to hazardous levels of noise, experience temporary hearing loss after officiating games, and a hearing conservation program is warranted. Further temporary threshold shift research has the potential to identify officials of other sporting events that are at an increased risk of noise-induced hearing loss.

Evidence of "hidden hearing loss" following noise exposures that produce robust TTS and ABR wave-I amplitude reductions

In animals, noise exposures that produce robust temporary threshold shifts (TTS) can produce immediate damage to afferent synapses and long-term degeneration of low spontaneous rate auditory nerve fibers. This synaptopathic damage has been shown to correlate with reduced auditory brainstem response (ABR) wave-I amplitudes at suprathreshold levels. The perceptual consequences of this "synaptopathy" remain unknown but have been suggested to include compromised hearing performance in competing background noise. Here, we used a modified startle inhibition paradigm to evaluate whether noise exposures that produce robust TTS and ABR wave-I reduction but not permanent threshold shift (PTS) reduced hearing-in-noise performance. Animals exposed to 109 dB SPL octave band noise showed TTS >30 dB 24-h post noise and modest but persistent ABR wave-I reduction 2 weeks post noise despite full recovery of ABR thresholds. Hearing-in-noise performance was negatively affected by the noise exposure. However, the effect was observed only at the poorest signal to noise ratio and was frequency specific. Although TTS >30 dB 24-h post noise was a predictor of functional deficits, there was no relationship between the degree of ABR wave-I reduction and degree of functional impairment.

Application of Mouse Models to Research in Hearing and Balance

Laboratory mice (Mus musculus) have become the major model species for inner ear research. The major uses of mice include gene discovery, characterization, and confirmation. Every application of mice is founded on assumptions about what mice represent and how the information gained may be generalized. A host of successes support the continued use of mice to understand hearing and balance. Depending on the research question, however, some mouse models and research designs will be more appropriate than others. Here, we recount some of the history and successes of the use of mice in hearing and vestibular studies and offer guidelines to those considering how to apply mouse models.

Human fatigue and the crash of the airship Italia

The airship Italia, commanded by General Umberto Nobile, crashed during its return flight from the North Pole in 1928. The cause of the accident was never satisfactorily explained. We present evidence that the crash may have been fatigue-related. Nobile's memoirs indicate that at the time of the crash he had been awake for at least 72 h. Sleep deprivation impairs multiple aspects of cognitive functioning necessary for exploration missions. Just prior to the crash, Nobile made three command errors, all of which are of types associated with inadequate sleep. First, he ordered a release of lift gas when he should have restarted engines (an example of incorrect data synthesis, with deterioration of divergent thinking); second, he inappropriately ordered the ship above the cloud layer (a deficiency in the assessment of relative risks); and third, he remained above the cloud layer for a prolonged period of time (examples of attention to secondary problems, and calculation problems). We argue that as a result of these three errors, which would not be expected from such an experienced commander, there was no longer enough static lift to maintain level flight when the ship went below the cloud layer. Applying Circadian Performance Simulation Software to the sleep-wake patterns described by Nobile in his memoirs, we found that the predicted performance for someone awake as long as he had been is extremely low. This supports the historical evidence that human fatigue contributed to the crash of the Italia.

Dietary supplement comprised of β-carotene, vitamin C, vitamin E, and magnesium: failure to prevent music-induced temporary threshold shift

This study examined potential prevention of music-induced temporary threshold shift (TTS) in normal-hearing participants. A dietary supplement composed of β-carotene, vitamins C and E, and magnesium was assessed using a randomized, placebo-controlled, double-blind study design. Dosing began 3 days prior to the music exposure with the final dose consumed approximately 30-min pre-exposure. There were no group differences in post-exposure TTS or music-induced decreases in distortion product otoacoustic emission (DPOAE) amplitude. Transient tinnitus was more likely to be reported by the treatment group, but there were no group differences in perceived loudness or bothersomeness. All subjects were monitored until auditory function returned to pre-exposure levels. Taken together, this supplement had no effect on noise-induced changes in hearing. Recommendations for future clinical trials are discussed.

Hepatocyte nuclear factor-4 alpha in noise-induced cochlear neuropathy

Noise-induced hearing loss (NIHL) is a problem of profound clinical significance and growing magnitude. Alarmingly, even moderate noise levels, previously assumed to cause only temporary shifts in auditory thresholds ("temporary" NIHL), are now known to cause cochlear synaptopathy and subsequent neuropathy. To uncover molecular mechanisms of this neuropathy, a network analysis of genes reported to have significantly altered expression after temporary threshold shift-inducing noise exposure was performed. The transcription factor Hepatocyte Nuclear Factor-4 alpha (HNF4α), which had not previously been studied in the context of cochlear response to noise, was identified as a hub of a top-ranking network. Hnf4α expression and localization using quantitative RT-PCR and in situ hybridization, respectively, were described in adolescent and adult mice exposed to neuropathic noise levels in adolescence. Isoforms α3 and α12 in the cochlea were also identified. At every age examined, Hnf4α mRNA expression in the cochlear apex was similar to expression in the base. Hnf4α expression was evident in select cochlear cells, including spiral ganglion neurons (SGNs) and hair cells, and was significantly upregulated from 6 to 70 weeks of age, especially in SGNs. This age-related Hnf4α upregulation was inhibited by neuropathic noise exposure in adolescence. Hnf4α silencing with shRNA transfection into auditory neuroblast cells (VOT-33) reduced cell viability, as measured with the MTT assay, suggesting that Hnf4α may be involved in SGN survival. Our results motivate future studies of HNF4α in cochlear pathophysiology, especially because HNF4α mutations and polymorphisms are associated with human diseases that may include hearing loss. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 76: 1374-1386, 2016.

Concurrent Acoustic Activation of the Medial Olivocochlear System Modifies the After-Effects of Intense Low-Frequency Sound on the Human Inner Ear

>Human hearing is rather insensitive for very low frequencies (i.e. below 100 Hz). Despite this insensitivity, low-frequency sound can cause oscillating changes of cochlear gain in inner ear regions processing even much higher frequencies. These alterations outlast the duration of the low-frequency stimulation by several minutes, for which the term 'bounce phenomenon' has been coined. Previously, we have shown that the bounce can be traced by monitoring frequency and level changes of spontaneous otoacoustic emissions (SOAEs) over time. It has been suggested elsewhere that large receptor potentials elicited by low-frequency stimulation produce a net Ca(2+) influx and associated gain decrease in outer hair cells. The bounce presumably reflects an underdamped, homeostatic readjustment of increased Ca(2+) concentrations and related gain changes after low-frequency sound offset. Here, we test this hypothesis by activating the medial olivocochlear efferent system during presentation of the bounce-evoking low-frequency (LF) sound. The efferent system is known to modulate outer hair cell Ca(2+) concentrations and receptor potentials, and therefore, it should modulate the characteristics of the bounce phenomenon. We show that simultaneous presentation of contralateral broadband noise (100 Hz-8 kHz, 65 and 70 dB SPL, 90 s, activating the efferent system) and ipsilateral low-frequency sound (30 Hz, 120 dB SPL, 90 s, inducing the bounce) affects the characteristics of bouncing SOAEs recorded after low-frequency sound offset. Specifically, the decay time constant of the SOAE level changes is shorter, and the transient SOAE suppression is less pronounced. Moreover, the number of new, transient SOAEs as they are seen during the bounce, are reduced. Taken together, activation of the medial olivocochlear system during induction of the bounce phenomenon with low-frequency sound results in changed characteristics of the bounce phenomenon. Thus, our data provide experimental support for the hypothesis that outer hair cell calcium homeostasis is the source of the bounce phenomenon.

Genetic Polymorphisms Associated with Hearing Threshold Shift in Subjects during First Encounter with Occupational Impulse Noise

Noise-induced hearing loss (NIHL) is the most significant occupational health issue worldwide. We conducted a genome-wide association study to identify single-nucleotide polymorphisms (SNPs) associated with hearing threshold shift in young males undergoing their first encounter with occupational impulse noise. We report a significant association of SNP rs7598759 (p < 5 x 10(-7); p = 0.01 after permutation and correction; Odds Ratio = 12.75) in the gene coding for nucleolin, a multifunctional phosphoprotein involved in the control of senescence and protection against apoptosis. Interestingly, nucleolin has been shown to mediate the anti-apoptotic effect of HSP70, a protein found to prevent ototoxicity and whose polymorphisms have been associated with susceptibility to NIHL. Increase in nucleolin expression has also been associated with the prevention of apoptosis in cells undergoing oxidative stress, a well-known metabolic sequela of noise exposure. To assess the potential role of nucleolin in hearing loss, we tested down-regulation of nucleolin in cochlear sensory cells HEI-OC1 under oxidative stress conditions and report increased sensitivity to cisplatin, a chemotherapeutic drug with ototoxic side effects. Additional SNPs were found with suggestive association (p < 5 x 10(-4)), of which 7 SNPs were located in genes previously reported to be related to NIHL and 43 of them were observed in 36 other genes previously not reported to be associated with NIHL. Taken together, our GWAS data and in vitro studies reported herein suggest that nucleolin is a potential candidate associated with NIHL in this population.

Noise-induced hearing loss: a recreational noise perspective

PURPOSE OF REVIEW

This review will discuss the real-world risk factors involved in noise-induced hearing loss as a result of common and popular recreational activities prone to mid and high levels of noise exposure. Although there are currently no interventional measures available to reverse or mitigate preexisting hearing loss from noise, we discuss the vital importance of hearing loss prevention from noise exposure avoidance and reduction.

RECENT FINDINGS

Despite a seeming understanding of the effects of noise exposure from various recreational activities and devices, a large percentage of the general public who is at risk of such noise-induced hearing loss still chooses to refrain from using hearing protection instruments.

SUMMARY

While occupational exposures pose the greatest traditional risk to hearing conservation in selected workers, recreational risk factors for noise-induced hearing loss may be more insidious in overall effect given the indifferent attitude of much of the general public and particularly our youths toward hearing protection during recreational activities. Active counseling regarding the consequences of excessive noise exposure and the potential benefits to hearing from usage of hearing protection instruments is critical to providing best possible care in the hearing health professions.

Immediate and delayed cochlear neuropathy after noise exposure in pubescent mice

Moderate acoustic overexposure in adult rodents is known to cause acute loss of synapses on sensory inner hair cells (IHCs) and delayed degeneration of the auditory nerve, despite the completely reversible temporary threshold shift (TTS) and morphologically intact hair cells. Our objective was to determine whether a cochlear synaptopathy followed by neuropathy occurs after noise exposure in pubescence, and to define neuropathic versus non-neuropathic noise levels for pubescent mice. While exposing 6 week old CBA/CaJ mice to 8-16 kHz bandpass noise for 2 hrs, we defined 97 dB sound pressure level (SPL) as the threshold for this particular type of neuropathic exposure associated with TTS, and 94 dB SPL as the highest non-neuropathic noise level associated with TTS. Exposure to 100 dB SPL caused permanent threshold shift although exposure of 16 week old mice to the same noise is reported to cause only TTS. Amplitude of wave I of the auditory brainstem response, which reflects the summed activity of the cochlear nerve, was complemented by synaptic ribbon counts in IHCs using confocal microscopy, and by stereological counts of peripheral axons and cell bodies of the cochlear nerve from 24 hours to 16 months post exposure. Mice exposed to neuropathic noise demonstrated immediate cochlear synaptopathy by 24 hours post exposure, and delayed neurodegeneration characterized by axonal retraction at 8 months, and spiral ganglion cell loss at 8-16 months post exposure. Although the damage was initially limited to the cochlear base, it progressed to also involve the cochlear apex by 8 months post exposure. Our data demonstrate a fine line between neuropathic and non-neuropathic noise levels associated with TTS in the pubescent cochlea.

Partial to complete suppression of unilateral noise-induced tinnitus in rats after cyclobenzaprine treatment

Some forms of tinnitus are believed to arise from abnormal central nervous system activity following a single or repeated noise exposure, for which there are no widely accepted pharmacological treatments. One central site that could be related to tinnitus awareness or modulation is the locus coeruleus, a brainstem structure associated with stress, arousal, and attention. In the present study, we evaluated the effects of cyclobenzaprine, a drug known to act on the rat locus coeruleus, on noise-induced tinnitus using Gap Prepulse Inhibition of the Acoustic Startle (GPIAS). In untreated rats, brief silent gaps presented prior to a 5-10-kHz bandpass startling stimulus produced robust GPIAS. Treatment with cyclobenzaprine alone had no effect on the ability of gaps to suppress the startle response. When animals were exposed to intense narrow-band (126 dB SPL, 16 kHz, 100 Hz BW) unilateral noise, GPIAS was significantly reduced, suggesting the presence of tinnitus. Following the noise exposure, a subset of rats that maintained a robust startle response continued to show GPIAS impairment at 6-20 kHz, 40 days post-noise, suggesting chronic tinnitus. When this subset of animals was treated with cyclobenzaprine, at a dose that had no significant effects on the startle response (0.5 mg/kg), GPIAS recovered partially or to near baseline levels at the affected frequencies. These results were consistent with the absence of tinnitus. By 48 h post-treatment, evidence of tinnitus re-emerged. Our results suggest that cyclobenzaprine was effective in transiently suppressing noise-induced tinnitus in rats.

Temporary threshold shift after impulse-noise during video game play: laboratory data

OBJECTIVE

Prevention of temporary threshold shift (TTS) after laboratory-based exposure to pure-tones, broadband noise, and narrowband noise signals has been achieved, but prevention of TTS under these experimental conditions may not accurately reflect protection against hearing loss following impulse noise. This study used a controlled laboratory-based TTS paradigm that incorporated impulsive stimuli into the exposure protocol; development of this model could provide a novel platform for assessing proposed therapeutics.

DESIGN

Participants played a video game that delivered gunfire-like sound through headphones as part of a target practice game. Effects were measured using audiometric threshold evaluations and distortion product otoacoustic emissions (DPOAEs). The sound level and number of impulses presented were sequentially increased throughout the study.

STUDY SAMPLE

Participants were normal-hearing students at the University of Florida who provided written informed consent prior to participation.

RESULTS

TTS was not reliably induced by any of the exposure conditions assessed here. However, there was significant individual variability, and a subset of subjects showed TTS under some exposure conditions.

CONCLUSIONS

A subset of participants demonstrated reliable threshold shifts under some conditions. Additional experiments are needed to better understand and optimize stimulus parameters that influence TTS after simulated impulse noise.